fix(install): remove OPENSHELL_INSTALL_METHOD variable #2654

Job	Run time
Resolve PR metadata	7s
build-cli / Resolve build plan	2s
build-gateway / Resolve build plan	4s
build-supervisor / Resolve build plan	2s
build-cli / Rust cli (amd64) / cli (amd64)	13m 13s
build-supervisor / Rust sandbox (amd64) / sandbox (amd64)	3m 38s
build-supervisor / Rust sandbox (arm64) / sandbox (arm64)	3m 47s
build-gateway / Rust gateway (amd64) / gateway (amd64)	6m 53s
build-gateway / Rust gateway (arm64) / gateway (arm64)	7m 17s
build-supervisor / Build supervisor (arm64)	1m 25s
build-supervisor / Build supervisor (amd64)	1m 29s
build-supervisor / Merge supervisor manifest	1m 9s
build-gateway / Build gateway (amd64)	1m 35s
build-gateway / Build gateway (arm64)	1m 32s
gpu-e2e	0s
GPU E2E result	0s
build-gateway / Merge gateway manifest	1m 5s
e2e / E2E (rust-podman-rootless, ubuntu-24.04)	17m 57s
e2e / E2E (rust-podman-rootless, ubuntu-26.04)	18m 25s
e2e / E2E (mcp)	6m 42s
e2e / E2E (python)	6m 57s
kubernetes-e2e (v1beta1, v0.5.0, combined) / Kubernetes E2E (Rust smoke, combined, Agent Sandbox v1beta1)	9m 45s
e2e / E2E (rust-docker)	8m 16s
kubernetes-e2e (v1beta1, v0.5.0, sidecar, deploy/helm/openshell/ci/values-sidecar.yaml) / Kubernetes E2E (Rust smoke, sidecar, Agent Sandbox v1beta1)	9m 26s
kubernetes-e2e (v1alpha1, v0.4.6, combined) / Kubernetes E2E (Rust smoke, combined, Agent Sandbox v1alpha1)	9m 39s
kubernetes-ha-e2e	-1s
Kubernetes HA E2E result	-1s
build-cli / Build ${{ inputs.component }} (${{ matrix.arch }})	-1s
build-cli / Merge ${{ inputs.component }} manifest	-1s
Core E2E result	5s
	2h 10m 26s

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